The long-term goal of this research is to advance our knowledge of how the brain combines the information of multiple sensory systems coding for spatial orientation and how adaptation to vestibular imbalance influences spatial orientation. In healthy human subjects verticality perception is accurate while upright. After prolonged roll-tilt, humans show a systematic bias in perceived direction towards the previous roll-tilted position (so-called "post-tilt bias"). Here we evaluate different potential explanations for this bias using both vision-dependent and vision-independent paradigms of verticality perception.